246TAKING UP OF POLLEN BY INSECTS.sap. Sometimes little drops of nectar are also secreted by the cells composing thesehairs. Certain small bees of the genus And/rena are in the habit of entering thecavity to feast on the hairs. Three ways are open to them, viz. the two smaUorifices in the background on either side of, and close to, the column, and the largeoval opening in the middle ofthe slipper and in front of thecolumn. They choose the las<>and shp under the broad, roughstigma to the bottom of theslipper where they feed on thosucculent cells of the hairs. Aftera time they wish to escape iutnthe open air again, but that isnot so easy. The edges of thelarge central opening are inflected(see fig. 267 ^), and so fashionedas to be unscalable, and the beeshave no choice but to makeuse of one of the two littleexits at the back of the slipper.Fig. 265.—Contrivances for loading insects with pollen.1 Flower of an Iris (Iris Germaniaa), with three segments of the perianth reflexed and three erect. On each of the former is a strip of yellow hairs which stand out conspicuously from the violet background of the perianth-segment, and serves as a guide to insects entering the honey-containmg tube of the perianth. 2 Upper half of the perianth-tube showing the three passages leading to the honey. Above each passage is a stamen with a long, linear anther facing outwards, and arching over each stamen is one of the three bl-lobed petaloid stigmas. The perianth-lobes have been removed.Even through these escape is not altogether easy, the bees being obhged to squeezethrough the narrow opening. The result is that one shoulder brushes against thesoft, viscid pollen of the anther which forms the inner border of the orifice. Thelast act in the story is the entrance of the insect with its shoulder covered withpollen into another Gypripedium flower, whose rough stigma is thereupon imme¬diately besmeared with pollen.